BACKGROUND: Fast track rehabilitation after primary total hip (THR) and total knee replacement (TKR) is gaining popularity. We performed a prospective clinical trial to identify predictive factors for successful fast track rehabilitation. METHODS: Between June 2005 and January 2006, 52 THR and 48 TKR were performed on consecutive patients off the local waiting list with no pre-selection or exclusion criteria. Patients underwent a fast track rehabilitation programme within a group-dynamic set-up aiming for discharge day 3 to 5 postoperatively. Demographic, clinical and social factors were analysed. RESULTS: Eighty-four percent (n = 44) of THR patients and 73% (n = 35) following TKR achieved the target discharge. Average discharge after THR was 5.4 and 5.5 days after TKR. Delayed discharge was mostly related to medical, social and organisational reasons. Age, 3 m-get-up-and-go-test (3 m-TGUGT), home situation and preoperative walking distance were the main predictors for the early discharge after THR; age, diagnosis, ASA class and preoperative pain medication were influential for TKR. Perioperative complication rates were within or below the national average. CONCLUSION: Successful fast track rehabilitation is possible without pre-selection and does not seem to compromise clinical safety. However, a good social and physiotherapy community set-up should be available. The identified predictive factors could be helpful to identify candidates for fast track rehabilitation.